The present invention relates to a communication device employed in a communication system whereby a data processing center and data generating source are linked, in the case where data generating sources are arranged linearly; typical examples of such a communication system in which data generating sources are arranged linearly include a road management system, railway management system, sewer management system, airfield management system, river management system, or underground railway management system.
In a road management system, a management center is provided within the management zone and video cameras and/or vehicle sensors etc. are disposed along the roads in the management zone, the information from these being collected at the management center. Also, electro-optic display panels are disposed along the roads. Information concerning accidents and/or congestion from adjacent management zones is collected at the management center and evaluation of various types is performed using these items of information and the information of the management zone in question; as a result, various kinds of guidance including congestion information etc. are displayed on electro-optic notice boards, thereby performing traffic management.
Taking the example of such a road management system, conventionally, information was collected by connecting an information generating source and the center by a one-to-one communication line, and guidance was displayed on the electro-optic notice board.
Such a method suffered from the problem of lack of flexibility owing to the following.
For example, if it was desired to add a new camera in a road management zone, construction work had to be undertaken to lay the communication line to the management center from the point where the addition was made. The same problem arose if it was desired to move a camera.
Roads constitute infrastructure that is used for a long period. New and superior monitoring devices make their appearance from time to time. Thus, there is the problem that construction work for laying communication lines arose every time a new type of device was introduced.
Although monitoring is performed by machines insofar as it can be, monitoring by human beings having the five senses may still be necessary. This is the case when slight changes of sound or changes in the atmosphere etc. are to be monitored. These may necessitate patrolling by human beings. In such cases, the monitoring staff have to perform monitoring by patrolling by carrying portable terminals. The monitoring staff need to communicate with the center by their portable terminals from time to time. With the conventional method, preparatory work was necessary to arrange connectors at various locations along the road, these connectors being linked to the center by communication lines. This was not particularly practical.
This information that it was desired to send was of various types, ranging from large amounts of information for which real-time characteristics were required such as video or small quantities of information that did not require real time characteristics, such as monitoring data. It is desirable for these to be integrated and sent by a number of cables if possible.
A further problem with the conventional method was that communication became impossible if there was some fault in the communication device or communication line.
Thus, the conventional system suffered from inflexibility in regard to alterations such as addition or movement of data generating sources or installation of temporary data sources. It also lacked the capability of being able to freely adapt to transmission data of various types such as ITV image data, computer data, or audio data etc. and to send these various types of data in integrated manner. Furthermore, while self-recovery would be desirable in the event of occurrence of a fault, such a function cannot be expected with the conventional system in which data generating sources and the center are connected by cable. Furthermore, from the point of view of infrastructure, there are many problems with the conventional system in that the communication system must be flexibly adapted to alterations over a long period.
An object of the present invention is to realize a communication system wherein the above problems can be solved, which has considerable flexibility, which can cope with data of various types, which can also cope with faults, and which can flexibly cope with future improvements in equipment.